In the production of pulp material to be used in the making of paper or other paper based packaging material. One conventional method is to employ a mechanical refiner. Mechanical refiners include, but are not limited to, refiners to process comminuted cellulosic material such as wood chips, etc. to produce pulp, and dispersers typically used in the processing of recycled paper material. Mechanical refiners typically include a set of opposing discs, such as a pair of flat discs at least one of which rotates, a pair of conically shaped discs, and an assembly of parallel flat and conical discs. As feed material moves through a gap between the opposing discs, fibers in the material are separated to produce refined pulp; ink, and other contaminates may be dispersed from paper to produced a recycle pulp material.
Mechanical refiners that produce pulp from wood chips and other comminuted cellulosic material, typically referred to as refiners, have plates with bars and grooves on the front face of their plates. The plates are mounted on opposing discs. The gap between plates with bars and grooves is typically planer and formed between the upper ridges of the bars on opposing plates. Mechanical refiners used to process recycled paper and paperboard material are typically referred to as dispergers or dispersers, and have plates with teeth on the front face of the plates. The gap between opposing plates in a disperser may have a serpentine shape formed by the intermeshing rows of teeth on the opposing front faces of the plates.
The refining or dispersing action occurs as feed material, e.g., wood chips or recycled paper, enters the gap between the discs through an opening in one of the plates. The feed material is driven by centrifugal force to move radially outwardly through the gap and between the front faces of the plates. The refining or dispersing surfaces on the front faces act on the feed material as the material moves through the gap and is subjected to pulsating forces due to the crossing of the bars or teeth on the plates.
Plates may be formed by an annular assembly of plate segments mounted on the discs. The plates are generally an annular array of plate segments, such as pie shaped segments. The segments are mounted side-by-side to form a circular plate mounted onto the disc mounting surface. The plates have a front face with bars and grooves forming refining surfaces in a pulp refiner or rows of teeth forming dispersing surfaces in a disperser. The gap in the refiner or disperser is formed between the front faces of the plates on the opposing discs. The back faces of the plates are mounted to a disc mounting surface. Bolts and other fasteners hold the plates to the disc mounting surface.
Plate segments, for a convention mechanical refiner (capable of handling high, medium or low consistency feed material) or a disperser (capable of handling recycled material feed material), are a critical component of the refining or dispersing equipment. As the feed material moves across the surface of the plate segments, the surface of the fronts of the plate segments wear down. The refining and dispersion action performed by the plate segments become less effective as the plates wear down. The worn plate segments must be replaced. Generally, plate segments are periodically replaced on refiners and dispersers.
A typical annular array of plate segments for a refiner or disperser includes three (3) to twenty four (24) equally-sized plate segments. At every plate change, all segments of an annular array of plate segments are removed and inspected, mounting surface (surface of the discs) cleaned, and the new segments installed. The plate segments that can be reused are cleaned and new segments are substituted for worn segments, typically all plate segments are replaced but there are times when some plate segments may be cleaned and reused. The cleaned and new segments are mounted one-by-one onto the disc mounting surface. The mounting of each segment requires a shimming process to maintain equal spacing between the segments. The mounting also involves applying a proper torque to the fastener securing the segments to the disc mounting surface.
Refiners and dispersers usually have two annular plates arranged opposite to each other in the refiner. In the twin refiners or twin dispersers, there may be four plates arranged in two opposing pairs of plates. The refiner or disperser may have one rotor (which may be a double-sided rotor in a twin refiner or disperser) facing a stationary stator. Alternatively, the refiner or disperser may have opposite counter-rotating rotors. Regardless of the specific disc configuration, the plate segments mounted to the discs are periodically replaced. Plate segment replacement is needed because the refining or dispersing surface on the segments wears down by the abrasiveness of the feed material rubbing against these surfaces. A worn refining or dispersing surface reduces the efficiency of the refiner or disperser.
Plate segments generally must be rigid and structurally strong. The plate segments must support the front faces that comprise many bars and grooves for refiners and teeth for dispersers, which are subjected to continuous refining or dispersing action of the abrasive feed material as they encounter the feed material, centrifugal forces in the refiner or disperser, and stresses from the fasteners, e.g., bolts, that affix the segments to the disc mounting surface. A minimum plate thickness is conventionally in a range of 1.0 to 1.5 inches (25 to 38 millimeters (mm)). Additionally, the back face of the plate segments conventionally have a network of raised ribs, posts surrounding the bolt holes and other raised structures to provide structural support to the segments and to provide abutments that seat against the disc mounting surface.
The thickness requirement and network of raised structures on the plate segments contribute substantially to the mass of the segments. The segments are formed by casting molding metal. The cast plate segments tend to have a large mass (i.e., heavy in weight), which makes the cast plate segments difficult to handle when replacement is necessary. The large mass of the plate segments increases the cost of casting due to the cost for a large amount of metal, cost of shipping and cost to handle and mount the segments to the disc. It is desirable to produce a plate segment using a less amount of metal while meeting the mounting and structural requirements needed for a structurally strong and rigid segment.